Engine Control System for Construction Machine

ABSTRACT

Disclosed is an engine control system for a construction machine having an engine and a control device for controlling, via a directional control valve, a flow of pressure oil to be fed to a hydraulic actuator. The system is provided with a controller, which includes a manipulation state determination unit for the control device and an idle stop control unit for performing idle stop control when the control device is determined to have remained unmanipulated. The system also includes a temperature sensing device for a fluid relevant to the operation of the engine. The controller includes a unit for determining whether or not the temperature of the fluid is not higher than a predetermined temperature. When the temperature of the fluid is determined to be not higher than the predetermined temperature, the controller disables the idle stop control.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of Japanese Patent Application2012-003295 filed Jan. 11, 2012, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an engine control system for a constructionmachine such as a hydraulic excavator, which after a predetermined timefrom the commencement of an idle operation state, can perform idle stopcontrol that automatically stops an operation of an engine.

2. Description of the Related Art

As a conventional technology of this kind, an engine control system fora working machine is disclosed in JP-A-2003-65097. This conventionaltechnology is equipped with a controller. This controller automaticallystops an operation of an engine when a single-touch operation pushbuttonswitch, that is, an idle stop switch is operated during idling of theengine, and also performs idle stop control to automatically stop theoperation of the engine when a state in which a control lever remainsunmanipulated has continued longer than a predetermined time.

SUMMARY OF THE INVENTION

With the above-mentioned conventional technology, a problem howevertends to arise when the working machine is placed under a workenvironment of low temperature to perform work. Under such a workenvironment of low temperature, the temperature of air is low, and as aconsequence, the temperature of working oil for driving a hydraulicactuator, the temperature of engine coolant for cooling the engine andthe temperature of fuel for the engine are lowered, so that the engineis prone to cooling. When the idle stop switch is operated and thecontrol lever is returned from a manipulated position, where work isbeing performed, to a neutral position to temporarily stop the work, theabove-mentioned conventional technology brings the engine to an idleoperation state in which the rpm of the engine is a predetermined lowrpm, and after an elapse of a predetermined time, performs idle stopcontrol to stop the operation of the engine even under such a workenvironment of low temperature.

Under a work environment of low temperature, however, an engine is hardto start when an attempt is made to start the engine for the resumptionof work after a while from stopping an operation of the engine asmentioned above, because the engine has been cooled. Therefore, a longercranking time is needed from an operation of a starter switch by anengine key until a start-up of the engine. Moreover, working oil of lowtemperature has a high viscosity, and therefore, needs a greater torquefor driving a hydraulic pump so that a greater load is exerted on theengine. In addition, fuel of low temperature leads to solidification ofwax components contained in the fuel, thereby inducing such waxcomponents to deposit on a fuel filter, and hence, lowering the feedcapability of fuel to the engine. Due to these causes, the enginebecomes hard to start as mentioned above.

With the conventional technology, a longer cranking time is needed asmentioned above when desired to resume the discontinued work under awork environment of low temperature after idle stop control wasperformed. Therefore, a greater power consumption is needed inconnection with this start-up of the engine, and an economical problemarises. Furthermore, a longer cranking time is required until the workcan be resumed, leading to problems that a sense of uncertainty is givento the operator and the work efficiency tends to decrease.

With the above-mentioned actual situation of the conventional technologyin view, the present invention has as an object thereof the provision ofan engine control system for a construction machine, which can save apower consumption relevant to a start-up of an engine under a workenvironment of low temperature and can also promptly resume work afterthe work is once stopped temporarily.

To achieve the above-described object, the present invention ischaracterized in that in an engine control system for a constructionmachine provided with an engine, a hydraulic pump drivable by theengine, a hydraulic actuator drivable by pressure oil delivered from thehydraulic pump, a directional control valve for controlling a flow ofpressure oil to be fed from the hydraulic pump to the hydraulicactuator, and a control device for switchingly controlling thedirectional control valve, and said engine control system being providedwith a controller, which includes a manipulation state determinationunit for determining a manipulation state of the control device and anidle stop control unit for performing idle stop control to stop anoperation of the engine when the control device is determined to haveremained unmanipulated for a predetermined time at the manipulationstate determination unit, the engine control system is provided with atemperature sensing device for detecting a temperature of a fluidrelevant to the operation of the engine, the controller comprises atemperature determination unit for determining whether or not thetemperature of the fluid as detected by the temperature sensing deviceis not higher than a predetermined temperature set beforehand, and, whenthe temperature of the fluid is determined to be not higher than thepredetermined temperature at the temperature determination unit, thecontroller performs processing to disable the idle stop control by theidle stop control unit.

According to the present invention constructed as described above, thecontroller performs processing to forcibly disable idle stop controlwhen the construction machine has performed work under a workenvironment of low temperature that is considered to pose a problem on astart-up of the engine, the control device is determined to haveremained unmanipulated for the predetermined time at the manipulationstate determination unit of the controller and a temperature detected bythe temperature sensing device is determined to be not higher than thepredetermined temperature at the temperature determination unit of thecontroller, although under such conditions, idle stop control is aboutto be performed.

Even when the control device is returned to a neutral position to oncestop work temporarily from a manipulated position where the work isbeing performed, the operation of the engine, therefore, continueswithout stopping. As a consequence, the present invention obviatesrestarting the engine, and moreover, guides working oil, engine coolantand engine fuel into circuits, whereby the engine is kept warm toprevent cooling of the engine which would otherwise occur due to theenvironment of low temperature. In other words, the present inventiondoes not require to restart the engine upon resumption of worksubsequent to its discontinuation even under a work environment of lowtemperature that is considered to pose a problem on a start-up of theengine, and therefore, can save a power consumption associated with anoperation of a starter switch and can also promptly resume work after itis once stopped temporarily.

The present invention may also be characterized in that in theabove-described invention, the controller is provided with an idleoperation control unit for holding an rpm of the engine at an idle rpm,which is a predetermined low rpm, when the control device is determinedby the manipulation state determination unit to have been brought from amanipulated state to an unmanipulated state, and the idle stop controlunit performs processing to stop the operation of the engine when thecontrol device is determined by the manipulation state determinationunit to have been unmanipulated for a predetermined time from a start ofidle operation control by the idle operation control unit.

According to the present invention constructed as described immediatelyabove, when the control device is returned to the neutral position toonce stop work temporarily from a manipulated position where the work isbeing performed, the engine moves to an idle operation by the idleoperation control unit of the controller, and the idle operation iscontinued until the work is resumed next. When the control device ismanipulated again from the neutral position in such a situation, theactual rpm of the engine promptly increases according to a target rpmfor the engine, thereby making it possible to perform work as desired.

The present invention may also be characterized in that in theabove-described invention, the fluid comprises working oil for drivingthe hydraulic actuator, and the temperature sensing device comprises atemperature sensor for detecting a temperature of the working oil.

The present invention may also be characterized in that in theabove-described invention, the fluid comprises engine coolant forcooling the engine, and the temperature sensing device comprises atemperature sensor for detecting a temperature of the engine coolant.

The present invention may also be characterized in that in theabove-described invention, the fluid comprises fuel for the engine, andthe temperature sensing device comprises a temperature sensor fordetecting a temperature of the fuel.

The present invention may also be characterized in that in theabove-described invention, the fluid comprises air in a work environmentwhere the construction machine is placed, and the temperature sensingdevice comprises a temperature sensor for detecting a temperature of theair to be introduced into an intake pipe of the engine.

The present invention is constructed such that the temperature sensingdevice is provided for detecting the temperature of the fluid relevantto the operation of the engine, the controller includes the temperaturedetermination unit for determining whether or not the temperature of thefluid as detected by the temperature sensing device is not higher thanthe predetermined temperature set beforehand and considered to pose aproblem on a start-up of the engine, and, when the temperature of thefluid is determined to be not higher than the predetermined temperatureat the temperature determination unit, the controller performsprocessing to disable the idle stop control by the idle stop controlunit. Owing to this construction, the present invention can save a powerconsumption relevant to a start-up of the engine under a workenvironment of low temperature, can assure excellent economy comparedwith before, can promptly resume work after the work is once stoppedtemporarily, can eliminate a sense of uncertainty conventionally tendedto be given to the operator, and compared with before, can also improvethe efficiency of work to be performed by the construction machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a hydraulic excavator mentioned as oneexample of a construction machine on which an embodiment of the enginecontrol system according to the present invention is arranged.

FIG. 2 is an electrical and hydraulic circuit diagram illustrating theembodiment of the engine control system according to the presentinvention.

FIG. 3 is a flowchart depicting primary processing steps to be executedat a controller arranged in the embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The embodiment of the engine control system according to the presentinvention for the construction machine will hereinafter be describedwith reference to the accompanying drawings.

The construction machine on which the engine control system according tothis embodiment is arranged is, for example, a hydraulic excavator shownin FIG. 1. This hydraulic excavator is provided with a travel base 1, arevolving upperstructure 2 mounted on the travel base 1, and workingequipment 3 attached pivotally in an up-and-down direction to therevolving upperstructure 2. The working equipment 3 includes a boom 4attached to the revolving upperstructure 2, an arm 5 connected to a freeend of the boom 4, and a bucket 6 connected to a free end of the arm 5.The working equipment 3 also includes a boom cylinder 4 a for actuatingthe boom 4, an arm cylinder 5 a for actuating the arm 5, and a bucketcylinder 6 a for actuating the bucket 6. An operator' s cab 7 isarranged at a front-side position of the revolving upperstructure 2, acounterweight 8 is arranged at a rear-side position of the revolvingupperstructure 2, and an engine compartment 9 is arranged between theoperator's cab 7 and the counterweight 8.

The engine control system according to this embodiment, which isarranged on the hydraulic excavator shown in FIG. 1, is provided with anengine 11 arranged in the engine compartment 9 and a hydraulic pump 12drivable by the engine 11. Also provided are a working oil reservoir 13for storing working oil to be fed to the hydraulic pump 12, a hydraulicactuator 14 collectively representing the above-mentioned boom cylinder4 a, arm cylinder 5 a and the like all of which are drivable by pressureoil delivered from the hydraulic pump 12, and a directional controlvalve 15 for controlling a flow of pressure oil to be fed from thehydraulic pump 12 to the hydraulic actuator 14.

In the operator's cab 7, a control device 16 is arranged. The controldevice 16 has a control lever 16 a to switchingly operate thedirectional control valve 15. This embodiment is also provided with atemperature sensing device for detecting a temperature of a fluidrelevant to an operation of the engine 11, for example, a temperaturesensor 20 for detecting a temperature of the working oil, a pressuresensor 21 for detecting whether or not the control lever 16 a of thecontrol device 16 has been manipulated, an instruction unit foroutputting an instruction signal that indicates performance ornon-performance of idle stop control to be mentioned subsequentlyherein, for example, an idle stop switch 22, and an rpm instructingdevice 23 for instructing a target rpm for the engine 11.

This embodiment is further provided with a control unit to be inputtedwith signals outputted from the temperature sensor 20, pressure sensor21, idle stop switch 22 and rpm instructing device 23, specifically acontroller 17.

As illustrated in FIG. 2, the controller 17 includes a neutraldetermination unit 17 a, an idle operation control unit 17 b, amanipulation determination unit 17 c, and an idle stop control unit 17d. The neutral determination unit 17 a determines, based on a signaloutputted from the pressure sensor 21, whether or not the control device16 has been returned from a manipulated position to a neutral position.The idle operation control unit 17 b holds the rpm of the engine 11 atan idle rpm, which is a predetermined low rpm, when the control device16 is determined to have been returned to the neutral position at theneutral determination unit 17 a. Based on signals outputted from thepressure sensor 21 during a predetermined time from a commencement ofidle operation control by the idle operation control unit 17 b, themanipulation determination unit 17 c determines whether or not thecontrol device 16 has been manipulated. The idle stop control unit 17 dperforms processing to stop the operation of the engine 11 when thecontrol device 16 is determined to have remained unmanipulated duringthe predetermined time at the manipulation determination unit 17 c. Itis to be noted that the manipulation state determination unit, whichdetermines the manipulation state of the control device 16, is made upby the above-mentioned neutral determination unit 17 a and manipulationdetermination unit 17 c.

The controller 17 also includes an idle stop determination unit 17 e fordetermining, according to a signal outputted from the idle stop switch22, performance or non-performance of idle stop control by the idle stopcontrol unit 17 d.

The controller 17 further includes a temperature determination unit 17 f. When the performance of idle stop control by the idle stop controlunit 17 d has been determined at the idle stop determination unit 17 eand the control device 16 is determined to have been returned to theneutral position at the neutral determination unit 17 a, the temperaturedetermination unit 17 f determines whether or not the temperature of theworking oil as detected by the temperature sensor 20 is not higher thanthe predetermined low temperature set beforehand and considered to posea problem on a start-up of the engine 11, for example, 0° C. When thetemperature of the working oil is determined to be not higher than thepredetermined low temperature at the temperature determination unit 17f, the controller 17 performs processing to disable idle stop control bythe idle stop control unit 17 d.

With reference to FIG. 3, a description will be made of primaryprocessing steps to be executed at the controller 17 in this embodiment,which is constructed as described above.

Upon performing digging work or the like by the hydraulic excavator, theidle stop switch 22 is held OFF or is switched to ON. According to asignal outputted from the idle stop switch 22, the idle stopdetermination unit 17 e of the controller 17 determines whether theperformance or non-performance of idle stop control has been instructed(step S1). When the idle stop switch 22 is OFF and the non-performanceof idle stop control has been instructed, normal operation control isperformed (step S2). Described specifically, when the control lever 16 aof the control device 16 is returned from a manipulated position to theneutral position, the idle operation control unit 17 b controls, basedon the determination by the neutral determination unit 17 a, to bringthe rpm of the engine 11 to an idle rpm, and in this idle operationstate, the operation of the engine 11 is continued. At this time, theidle stop control unit 17 d is held to remain non-functioning.

When the above-mentioned determination in step S1 finds that the idlestop switch 22 is set ON and the performance of idle stop control hasbeen instructed, the manipulation determination unit 17 c determines,based on signals outputted from the pressure sensor 21, whether or notthe control device 16 was manipulated during a predetermined time fromthe commencement of idle operation control by the idle operation controlunit 17 b (step S3). When the control device 16 is determined to havebeen manipulated, the routine moves to step S2, where normal operationcontrol is performed. Described specifically, the engine 11 is operatedsuch that the actual rpm of the engine 11 is brought to a target rpm forthe engine 11 as instructed by the rpm instructing device 23. At thistime, the directional control valve 15 is switched according tomanipulation of the control device 16. Accordingly, pressure oildelivered from the hydraulic pump 12 is fed to the hydraulic actuator 14via the directional control valve 15. The hydraulic actuator 14 is henceactuated to drive, for example, the working equipment 3 shown in FIG. 1so that digging work or the like of earth or sand is performed. When thecontrol lever 16 a of the control device 16 is returned to the neutralposition from such a manipulated position, the rpm of the engine 11drops to an idle operation state and this idle operation state iscontinued, as mentioned above.

When by the above-mentioned determination in step S3, the control device16 is determined to have remained unmanipulated, it is determined at thetemperature determination unit 17 f whether or not the temperature ofthe working oil as detected by the temperature sensor 20 is not higherthan the predetermined low temperature, for example, 0° C. (step S4) .When, the temperature of the working oil is determined to be higher thanthe predetermined low temperature, that is, 0° C., the routine moves tostep S5. In step S5, the idle stop control unit 17 d functions toperform processing that stops the operation of the engine 11. In otherwords, idle stop control is performed. In this case, resumption of thework needs to restart the engine 11. As this restart of the engine 11 isperformed in a work environment that the temperature of the working oilis held relatively high, the cranking time from an operation of thestarter switch until a start-up of the engine 11 can be shortened sothat no problem is imposed on the start-up of the engine 11.

When by the above-mentioned determination in step S4, the temperature ofthe working oil is determined to be not higher than the predeterminedlow temperature, for example, 0° C., it is indicated that the hydraulicexcavator is placed under a work environment of low temperature toperform work. The routine then moves to step S2 to perform normaloperation control. Described specifically, when the control lever 16 aof the control device 16 is returned from the manipulated position tothe neutral position, the rpm of the engine 11 is controlled to an idlerpm by the idle operation control unit 17 b, and under this idleoperation control, the operation of the engine 11 is continued. In otherwords, although the idle stop switch 22 is set ON to perform idle stopcontrol, the idle stop control is forcibly disabled.

According to the embodiment constructed as described above, when thehydraulic excavator is under a work environment of low temperature andthe control lever 16 a is returned from a manipulated position, wherework is being performed, to the neutral position to once stop the worktemporarily, the engine 11 moves to an idle operation by the idleoperation control unit 17 b of the controller 17, and this idleoperation is continued until the work is resumed next time. As aconsequence, this embodiment can obviates restarting the engine 11, andmoreover, can guide the working oil, engine coolant and fuel for theengine 11 into circuits, whereby cooling of the engine 11 due to theenvironment of low temperature is reduced. When the control lever 16 ais manipulated again from the neutral position, the actual rpm of theengine 11, therefore, promptly increases according to a target rpm forthe engine 11 so that desired work can be performed. Therefore, thisembodiment does not require to restart the engine 11 upon resuming workafter its temporary stop even under a work environment of lowtemperature that is considered to pose a problem on a start-up of theengine 11, and therefore, can save a power consumption associated withan operation of the starter switch and can assure excellent economy.Further, this embodiment can promptly resume work after it is oncestopped temporarily, can eliminate a sense of uncertainty that is tendedto be given to the operator, and can improve the efficiency of work tobe performed by the hydraulic excavator.

In the above-described embodiment, the temperature sensor 20 fordetecting the temperature of the working oil is arranged as thetemperature sensing device for detecting the temperature of the fluidrelevant to the operation of the engine 11. This invention shall,however, not be limited to such a construction. The present inventionmaybe constructed, for example, such that idle stop control is disabledirrespective of an ON operation of the idle stop switch 22 when atemperature sensor for detecting that the temperature of the enginecoolant is not higher than the predetermined low temperature, forexample, 0° C. is arranged as the temperature sensing device, thetemperature of the engine coolant is determined at the temperaturedetermination unit 17 f of the controller 17 as to whether or not it isnot higher than the predetermined low temperature, and the temperatureof the engine coolant is determined to be not higher than thepredetermined low temperature.

The present invention may also be constructed such that as thetemperature sensing device, a temperature sensor for detecting that thetemperature of the fuel for the engine 11 is not higher than thepredetermined low temperature, for example, 0° C. is arranged, thetemperature of the fuel is determined at the temperature determinationunit 17 f of the controller 17 as to whether or not it is not higherthan the predetermined low temperature, and idle stop control isdisabled irrespective of an ON operation of the idle stop switch 22 whenthe temperature of the fuel is determined to be not higher than thepredetermined temperature.

The present invention may also be constructed such that as thetemperature sensing device, a temperature sensor for detecting that thetemperature of air to be guided to an intake pipe of the engine 11, thatis, the air in a work environment where the hydraulic excavator isplaced is not higher than the predetermined low temperature, forexample, 0° C. is arranged, the temperature of the air is determined atthe temperature determination unit 17 f of the controller 17 as towhether or not it is not higher than the predetermined low temperature,and idle stop control is disabled irrespective of an ON operation of theidle stop switch 22 when the temperature of the air is determined to benot higher than the predetermined temperature.

1. An engine control system for a construction machine provided with anengine, a hydraulic pump drivable by the engine, a hydraulic actuatordrivable by pressure oil delivered from the hydraulic pump, adirectional control valve for controlling a flow of pressure oil to befed from the hydraulic pump to the hydraulic actuator, and a controldevice for switchingly controlling the directional control valve, andsaid engine control system being provided with a controller, whichincludes a manipulation state determination unit for determining amanipulation state of the control device and an idle stop control unitfor performing idle stop control to stop an operation of the engine whenthe control device is determined to have remained unmanipulated for apredetermined time at the manipulation state determination unit, whereinthe engine control system is provided with a temperature sensing devicefor detecting a temperature of a fluid relevant to the operation of theengine, the controller comprises a temperature determination unit fordetermining whether or not the temperature of the fluid as detected bythe temperature sensing device is not higher than a predeterminedtemperature set beforehand, and, when the temperature of the fluid isdetermined to be not higher than the predetermined temperature at thetemperature determination unit, the controller performs processing todisable the idle stop control by the idle stop control unit.
 2. Theengine control system according to claim 1, wherein: the controller isprovided with an idle operation control unit for holding an rpm of theengine at an idle rpm, which is a predetermined low rpm, when thecontrol device is determined by the manipulation state determinationunit to have been brought from a manipulated state to an unmanipulatedstate, and the idle stop control unit performs processing to stop theoperation of the engine when the control device is determined by themanipulation state determination unit to have been unmanipulated for apredetermined time from a start of idle operation control by the idleoperation control unit.
 3. The engine control system according to claim1, wherein: the fluid comprises working oil for driving the hydraulicactuator, and the temperature sensing device comprises a temperaturesensor for detecting a temperature of the working oil.
 4. The enginecontrol system according to claim 1, wherein: the fluid comprises enginecoolant for cooling the engine, and the temperature sensing devicecomprises a temperature sensor for detecting a temperature of the enginecoolant.
 5. The engine control system according to claim 1, wherein: thefluid comprises fuel for the engine, and the temperature sensing devicecomprises a temperature sensor for detecting a temperature of the fuel.6. The engine control system according to claim 1, wherein: the fluidcomprises air in a work environment where the construction machine isplaced, and the temperature sensing device comprises a temperaturesensor for detecting a temperature of the air to be introduced into anintake pipe of the engine.
 7. The engine control system according toclaim 2, wherein: the fluid comprises working oil for driving thehydraulic actuator, and the temperature sensing device comprises atemperature sensor for detecting a temperature of the working oil. 8.The engine control system according to claim 2, wherein: the fluidcomprises engine coolant for cooling the engine, and the temperaturesensing device comprises a temperature sensor for detecting atemperature of the engine coolant.
 9. The engine control systemaccording to claim 2, wherein: the fluid comprises fuel for the engine,and the temperature sensing device comprises a temperature sensor fordetecting a temperature of the fuel.
 10. The engine control systemaccording to claim 2, wherein: the fluid comprises air in a workenvironment where the construction machine is placed, and thetemperature sensing device comprises a temperature sensor for detectinga temperature of the air to be introduced into an intake pipe of theengine.